PROJECT SUMMARY/ABSTRACT Numbers of individuals living with cancer are fast growing, reaching 19 million by 2024. More than 50% of cancer survivors live with multiple concurrent symptoms after treatment completion. There is immediate need for effective strategies that can manage multiple symptoms simultaneously. Linkages between circadian aberrations and cancer-associated symptoms are supported by the current literature and our preliminary data. Therapeutic bright light has shown effectiveness in treating circadian rhythm sleep disorders and alleviating various symptoms associated with circadian aberrations. Although previous trials have shown that morning bright light prevented fatigue and quality of life from worsening during and after chemotherapy, those observed effects may have been compromised because individual differences in circadian patterns were not considered. The objective of this pilot study is to evaluate the feasibility of implementing a personalized bright light intervention and to estimate the effects of bright light on 4 common long-term or late effects of cancer (sleep disturbance, fatigue, depression, and cognitive dysfunction) and on quality of life in post-treatment survivors of breast cancer. To test our hypothesized mechanism, effects of bright light on circadian rhythms will also be examined. The long term goal is to identify the therapeutic effect of bright light and to develop effective interventions to attenuate multiple symptoms associated with cancer that are feasible for patient self- management. The specific aims are: 1) To assess the feasibility of implementing a home-based, personalized bright light intervention and the proposed data collection plan; 2) To estimate the effect of bright light on sleep disturbance, fatigue, depression, cognition, and quality of life, and 3) on circadian rhythms, in survivors of breast cancer. This randomized, controlled pilot study will recruit 34 female survivors with Stage I-III breast cancer. The participants will be randomized to either 30-minute blue-green light therapy at 12,000 lux or dim red light control at 5 lux. Light will be self-administered using a light visor cap at home for 14 consecutive days. Tailored to the individual's circadian pattern, light will be delivered either within 30 minutes of waking in the morning or between 1900-2000 hours in the evening. The nocturnal sleep patterns will be monitored by all- night in-lab polysomnography; sleep quality, fatigue, depression, and quality of life will be self-reported; cognition will be objectively assessed before and after the intervention. Circadian rhythm will be indexed by nocturnal core body temperature before and after the intervention. Feasibility will be determined by the proportion of contacted, recruited, and retained subjects, and completeness of the data collected. Subjective feedback and burden will be assessed at study exit.